SLEPS First Results from SLEPS A. Walser, M. Arpagaus, C. Appenzeller, J. Quiby MeteoSwiss

SLEPS COSMO General Meeting, 2003, Langen 1 SLEPS SLEPS: Short-range limited-area ensemble prediction system. Within project ‘Extreme Events’ of the Swiss national research project NCCR. Strategy bases on an adapted COSMO-LEPS for the short-range. Should be considered as a first step towards a short-range EPS. The smaller scales resolved in SLEPS implies the consideration of alternative growth mechanisms beyond the baroclinic growth accounted for by the SV analysis.  Strategies for the definition of optimal small-scale perturbations have to be found.

SLEPS COSMO General Meeting, 2003, Langen 2 SLEPS: Short-range adaptation of COSMO-LEPS Start of COSMO-LEPS integrations ? members COSMO-LEPS clustering times short-range clustering times number of RMs? horizontal resolution? day: 12 n-1 12 n+2 12 n+3 12 n+4 12 n+5 12 n+1 12 n 00 moist? EPS

SLEPS COSMO General Meeting, 2003, Langen 3 SLEPS: current setup 50+1 members 5 representative members (RMs) 5 Lokal Modell (limited-area) integrations nested into 5 RMs SLEPS: Short-range limited-area Ensemble Prediction System 5 clusters Hierarchical Cluster Analysis area: Europe fields: 4 variables (U,V,Q,Z) at 3 levels (500, 700, 850) for 3 time steps (24h, 48h, 72 h), number of clusters: fixed to 5 Representative Member Selection one per cluster: member nearest (3D) to the mean of its own cluster AND most distant to the other clusters’ means Global ECMWF EPS ensembles with moist singular vectors

SLEPS COSMO General Meeting, 2003, Langen 4 SLEPS: model domain with topography 10 km mesh-size horizontally, 32 vertical levels.

SLEPS COSMO General Meeting, 2003, Langen 5 Moist vs. operational singular vectors Coutinho et al. (2003) ‚opr‘ SVs (T42L31, OTI 48 h): linearized physics package with surface drag simple vertical diffusion ‚moist‘ SVs (T63L31, OTI 24 h): linearized physics package includes additionally: gravity wave drag long-wave radiation deep cumulus convection large-scale condensation  moist SVs: use of moist processes during SV evolution, but same norm (‚total energy norm‘)  no humidity perturbations.

SLEPS COSMO General Meeting, 2003, Langen 6 2 case studies: Storm Lothar (“Christmas Storm”): 26 December 1999 moist SV ECMWF EPS  SLEPS UTC, + 72 h opr SV ECMWF EPS  SLEPS UTC, + 72 h Storm Martin: 27/28 December 1999 moist SV EPS ECMWF  SLEPS UTC, + 72 h opr SV EPS ECMWF  SLEPS UTC, + 72 h

SLEPS COSMO General Meeting, 2003, Langen 7 Mean RMS error hPa of ECMWF EPS to opr analysis in SLEPS domain RMS ENS [m] Forecast time [h] red: opr SVs EPS blue: moist SVs EPS solid: Storm Lothar dotted: Storm Martin y: predicted value o: values of analysis N: number of members I: number of grid points

SLEPS COSMO General Meeting, 2003, Langen 8 Storm Lothar: probability forecast of SLEPS for 10 m wind gusts moist SVs opr SVs ECMWF opr analysis Lothar

SLEPS COSMO General Meeting, 2003, Langen 9 Lothar: 6 hours later… moist SVs opr SVs

SLEPS COSMO General Meeting, 2003, Langen 10 Lothar: again 6 hours later… moist SVsopr SVs

SLEPS COSMO General Meeting, 2003, Langen 11 Lothar: again 6 hours later… moist SVsopr SVs

SLEPS COSMO General Meeting, 2003, Langen 12 Lothar: probability forecast for 10 m wind gusts over the 24 hours storm period moist SVsopr SVs  Both ensemble quite similar.  Moist SVs SLEPS predicts a higher risk for strong wind gusts over northern France.

SLEPS COSMO General Meeting, 2003, Langen 13 Lothar: ECMWF EPS using only LEPS representative members over the 24 hours storm period moist SVs opr SVs Rather reduced probabilities compared to SLEPS in particular over the Atlantic.  SLEPS downscaling seems to be beneficial in this case.

SLEPS COSMO General Meeting, 2003, Langen 14 Lothar: ECMWF EPS using all 51 members over the 24 hours storm period moist SVs opr SVs Very similar  Effect of moist SVs not obvious.

SLEPS COSMO General Meeting, 2003, Langen 15 Storm Martin: probability forecast of SLEPS for 10 m wind gusts opr SVsmoist SVs Martin

SLEPS COSMO General Meeting, 2003, Langen 16 Storm Martin: 6 hours later… moist SVsopr SVs

SLEPS COSMO General Meeting, 2003, Langen 17 Storm Martin: 6 hours later… moist SVsopr SVs

SLEPS COSMO General Meeting, 2003, Langen 18 Storm Martin: 6 hours later… moist SVs opr SVs

SLEPS COSMO General Meeting, 2003, Langen 19 Storm Martin: probability forecast for 10 m wind gusts over the 24 hours storm period moist SVsopr SVs  moist SVs SLEPS predicts a risk in south-western France and northern Mediterranean Sea.  opr SVs SLEPS misses the storm.

SLEPS COSMO General Meeting, 2003, Langen 20 Martin: ECMWF EPS using only LEPS RMs over the 24 hours storm period moist SVsopr SVs  Provided risk from moist SVs ECMWF EPS lower over southwestern France and northern Mediterranean sea.  Opr SVs ECMWF EPS also misses the storm.

SLEPS COSMO General Meeting, 2003, Langen 21 Martin: ECMWF EPS using all 51 members over the 24 hours storm period moist SVsopr SVs Using all EPS members, differences between moist and opr SVs EPS smaller  moist SVs SLEPS additionally favoured by the clustering procedure.

SLEPS COSMO General Meeting, 2003, Langen 22 Conclusions from first SLEPS simulations Wind gust prediction for storm Lothar: Effect of moist SVs in SLEPS and ECMWF EPS small. Downscaling effect with SLEPS beneficial but not crucial. Wind gust prediction for storm Martin: Effect of moist SVs clearly positive both in SLEPS and ECMWF EPS. opr SVs SLEPS does not provide a storm warning. Downscaling effect with moist SVs SLEPS beneficial.